There have been known, as positive electrodes capable of forming a lithium battery having a high electromotive force, positive electrodes using LiCoO.sub.2 as an active material. The group of the present inventors has found an active material comprising at least one member selected from the group of lithium phosphates, lithium-cobalt phosphates, cobalt oxides and lithium-cobalt oxides, wherein lithium, cobalt and phosphorus are contained in a proportion of more than 0.1 mole of cobalt and more than 0.2 mole of phosphorus both per mole of lithium.
The novel active material having the composition as mentioned above is characterized in that it also comprises phosphorus besides lithium, cobalt and oxygen. The addition of phosphorus leads to a less mass and increases lithium ion incorporation per unit weight, which ultimately results in increased capacities. By using said active material for a positive electrode, primary or secondary lithium batteries superior in electromotive force, discharge voltage, discharge capacity and energy density, and having a still higher electromotive force than the conventional batteries using LiCoO.sub.2, can be obtained.